The present invention relates to a motor control system for a sewing machine in which thyristors are employed for motor driving control. More particularly, the invention relates to a brake and stop control system for a sewing machine.
Nowadays, sewing machines employ thyristors and their control systems for motor control. Such a system comprises a mechanical or electric brake means to stop the motor at a predetermined moment so as to stop the sewing needle at a predetermined "halt" position. The mechanical brake means is so complicated and has so many mechanical elements that the price of the sewing machine is relatively high. Precise "stop" control of the sewing needle at a predetermined halt position is relatively difficult by the electric brake means. Moreover the mechanical brake means is bulky and produces impact shock and noise. On the other hand, with the electric brake means, it is difficult to stop the sewing needle at the predetermined halt position quickly and correctly. Moreover, if the sewing needle is caught at its lowered position by a cloth, it can not move to its predetermined raised halt position. This overloads the motor winding and may destroy the motor.